This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Protein biosynthesis, or translation occurs on the ribosome, an RNA-protein complex conserved in all forms of life. Translation requires both the small and large subunits of the ribosome to work in concert. Therefore, our lab is studying the mechanism of the bacterial ribosome by determining x-ray crystal structures of ribosomal functional complexes. These complexes contain mRNA, tRNAs, antibiotics and translation factors trapped in different steps of protein synthesis. Presently, we are working on the structures of the ribosome in complexes with ribosome recycling factor (RRF) and with antibiotics that inhibit translocation and ribosome recycling.